Liquid crystal display device and method of fabricating the same

ABSTRACT

A reflective liquid crystal display device includes: first to fourth substrates spaced apart from and parallel to each other; a first stack including a first pixel electrode, a first alignment layer, a first common electrode, a second alignment layer and a first cholesteric liquid crystal layer between the first and second alignment layers; a second stack including a second pixel electrode, a third alignment layer, a second common electrode, a fourth alignment layer and a second cholesteric liquid crystal layer between the third and fourth alignment layers; a third stack including a third pixel electrode, a fifth alignment layer, a third common electrode, a sixth alignment layer and a third cholesteric liquid crystal layer between the fifth and sixth alignment layers; and a fourth stack including a first mode electrode, an ion storing layer, an electrolyte layer, an electrochromic layer and a second mode electrode sequentially on the first substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 16/688,591 filed on Nov. 19, 2019 which claims the priority benefitof Republic of Korea Patent Application No. 10-2018-0154638 filed inRepublic of Korea on Dec. 4, 2018, each of which is hereby incorporatedby reference in its entirety for all purposes as if fully set forthherein.

BACKGROUND Field of Technology

The present disclosure relates to a liquid crystal display device, andmore particularly, to a reflective liquid crystal display deviceincluding a cholesteric liquid crystal layer and an alignment layer dueto a self-alignment monomer and a method of fabricating the reflectiveliquid crystal display device.

Discussion of the Related Art

Recently, as the information age rapidly progresses, display devicesprocessing and displaying a large amount of information have advanced.For example, various flat panel displays (FPDs) having a thin profile, alight weight and a low power consumption have been researched.

As a result, a thin film transistor liquid crystal display (TFT-LCD)having an excellent color reproducibility and a thin profile has beendeveloped. The LCD device displays an image using an optical anisotropyand a polarization property of a liquid crystal molecule.

Specifically, display devices using a cholesteric liquid crystal (CLC)have been developed. For example, a reflective liquid crystal display(LCD) device where an image is displayed using three cholesteric liquidcrystal layers selectively reflecting red, green and blue colored lightswithout an additional backlight unit has been suggested.

In the stack type reflective LCD device, three stacks each including twosubstrates having alignment layers on inner surfaces thereof and acholesteric liquid crystal (CLC) layer are laminated. The three stacksselectively reflect red, green, and blue colored lights, respectively,to display an image.

First and second alignment layers may be formed on first and secondsubstrates, respectively, and a first cholesteric liquid crystal layerfor selective reflection of a red colored light may be formed betweenthe first and second alignment layers, thereby a first stack completed.Third and fourth alignment layers may be formed on third and fourthsubstrates, respectively, and a second cholesteric liquid crystal layerfor selective reflection of a green colored light may be formed betweenthe third and fourth alignment layers, thereby a second stack completed.Fifth and sixth alignment layers may be formed on fifth and sixthsubstrates, respectively, and a third cholesteric liquid crystal layerfor selective reflection of a blue colored light may be formed betweenthe fifth and sixth alignment layers, thereby a third stack completed.Next, a stack type reflective LCD device may be completed by attachingthe first, second and third stacks.

In the stack type reflective LCD device, since six substrates are usedand six alignment layers are formed, material cost increases and anumber of fabrication steps such as a rubbing increases. As a result, afabrication time and a fabrication cost increase.

In addition, since six alignment layers are individually formed and thenattached, optical axes of three cholesteric liquid crystal layers aremisaligned with each other. As a result, a contrast ratio and a colorpurity are reduced.

Further, a twist angle occurs due to an error of alignment directionsgenerated in an attachment step of three stacks. When a reactive mesogenis used to remedy the above drawback, a driving voltage increases.

Moreover, since each of six alignment layers has a thickness of about100 nm, a transmittance is reduced due to six alignment layers having atotal thickness of about 600 nm. When thicknesses of six alignmentlayers are reduced to prevent reduction of a transmittance, a defectoccurs due to decrease of an anchoring energy or a stain occurs due toinjection or dispensing of a cholesteric liquid crystal.

SUMMARY

Accordingly, the present disclosure is directed to a liquid crystaldisplay device that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

An object of the present disclosure is to provide a reflective liquidcrystal display device and a method of fabricating the same where afabrication process is simplified and a fabrication cost is reduced byforming an alignment layer through a single irradiation of anultraviolet ray after a cholesteric liquid crystal layer is formed.

Another object of the present disclosure is to provide a reflectiveliquid crystal display device and a method of fabricating the same wherea misalignment of optical axes is reduced and a contrast ratio and acolor purity are improved by forming an alignment layer through a singleirradiation of an ultraviolet ray after a cholesteric liquid crystallayer is formed.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present disclosure, as embodied and broadly described herein, areflective liquid crystal display device includes: first, second, thirdand fourth substrates spaced apart from and parallel to each other, eachof the first, second, third and fourth substrates including a pluralityof pixels; a first stack including a first pixel electrode in each ofthe plurality of pixels on an upper surface of the first substrate, afirst alignment layer on an entire surface including the first pixelelectrode, a first common electrode on an entire lower surface of thesecond substrate, a second alignment layer on an entire surfaceincluding the first common electrode and a first cholesteric liquidcrystal layer between the first and second alignment layers; a secondstack including a second pixel electrode in each of the plurality ofpixels on an upper surface of the second substrate, a third alignmentlayer on an entire surface including the second pixel electrode, asecond common electrode on an entire surface of the third substrate, afourth alignment layer on an entire surface including the second commonelectrode and a second cholesteric liquid crystal layer between thethird and fourth alignment layers; a third stack including a third pixelelectrode in each of the plurality of pixels on an upper surface of thethird substrate, a fifth alignment layer on an entire surface includingthe third pixel electrode, a third common electrode on an entire lowersurface of the fourth substrate, a sixth alignment layer on an entiresurface including the third common electrode and a third cholestericliquid crystal layer between the fifth and sixth alignment layers; and afourth stack including a first mode electrode, an ion storing layer, anelectrolyte layer, an electrochromic layer and a second mode electrodesequentially on an entire lower surface of the first substrate.

In another aspect, a method of fabricating a reflective liquid crystaldisplay device includes: forming a first mode electrode, an ion storinglayer, an electrolyte layer, an electrochromic layer and a second modeelectrode sequentially on an entire lower surface of a first substrate;forming a first pixel electrode in each of a plurality of pixels on anupper surface of the first substrate; forming a first common electrodeon an entire lower surface of a second substrate; forming a second pixelelectrode in each of the plurality of pixels on an upper surface of thesecond substrate; forming a first cholesteric liquid crystal layerbetween the first and second substrates with a mixed material of a firstcholesteric liquid crystal molecule and a self-alignment monomer;forming a second common electrode on an entire lower surface of a thirdsubstrate; forming a third pixel electrode in each of the plurality ofpixels on an upper surface of the third substrate; forming a secondcholesteric liquid crystal layer between the second and third substrateswith a mixed material of a second cholesteric liquid crystal moleculeand the self-alignment monomer; forming a third common electrode on anentire lower surface of a fourth substrate; forming a third cholestericliquid crystal layer between the third and fourth substrates with amixed material of a third cholesteric liquid crystal molecule and theself-alignment monomer; and forming a first alignment layer between thefirst substrate and the first cholesteric liquid crystal layer, a secondalignment layer between the second substrate and the first cholestericliquid crystal layer, a third alignment layer between the secondsubstrate and the second cholesteric liquid crystal layer, a fourthalignment layer between the third substrate and the second cholestericliquid crystal layer, a fifth alignment layer between the thirdsubstrate and the third cholesteric liquid crystal layer and a sixthalignment layer between the fourth substrate and the third cholestericliquid crystal layer by irradiating a polarized ultraviolet ray onto thefirst, second and third cholesteric liquid crystal layers.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross-sectional view showing a reflective liquid crystaldisplay device according to an embodiment of the present disclosure;

FIG. 2A is a cross-sectional view showing reflection of a red coloredlight of a reflective liquid crystal display device according to anembodiment of the present disclosure;

FIG. 2B is a cross-sectional view showing reflection of a green coloredlight of a reflective liquid crystal display device according to anembodiment of the present disclosure;

FIG. 2C is a cross-sectional view showing reflection of a blue coloredlight of a reflective liquid crystal display device according to anembodiment of the present disclosure;

FIG. 3A is a cross-sectional view showing an opaque mode of a reflectiveliquid crystal display device according to an embodiment of the presentdisclosure;

FIG. 3B is a cross-sectional view showing a transparent mode of areflective liquid crystal display device according to an embodiment ofthe present disclosure; and

FIGS. 4A to 4F are cross-sectional views showing a method of fabricatinga reflective liquid crystal display device according to an embodiment ofthe present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentdisclosure, examples of which may be illustrated in the accompanyingdrawings. In the following description, when a detailed description ofwell-known functions or configurations related to this document isdetermined to unnecessarily cloud a gist of the inventive concept, thedetailed description thereof will be omitted. The progression ofprocessing steps and/or operations described is an example; however, thesequence of steps and/or operations is not limited to that set forthherein and may be changed as is known in the art, with the exception ofsteps and/or operations necessarily occurring in a particular order.Like reference numerals designate like elements throughout. Names of therespective elements used in the following explanations are selected onlyfor convenience of writing the specification and may be thus differentfrom those used in actual products.

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following example embodimentsdescribed with reference to the accompanying drawings. The presentdisclosure may, however, be embodied in different forms and should notbe construed as limited to the example embodiments set forth herein.Rather, these example embodiments are provided so that this disclosuremay be sufficiently thorough and complete to assist those skilled in theart to fully understand the scope of the present disclosure. Further,the present disclosure is only defined by scopes of claims.

A shape, a size, a ratio, an angle, and a number disclosed in thedrawings for describing embodiments of the present disclosure are merelyan example. Thus, the present disclosure is not limited to theillustrated details. Like reference numerals refer to like elementsthroughout. In the following description, when the detailed descriptionof the relevant known function or configuration is determined tounnecessarily obscure an important point of the present disclosure, thedetailed description of such known function or configuration may beomitted. In a case where terms “comprise,” “have,” and “include”described in the present specification are used, another part may beadded unless a more limiting term, such as “only,” is used. The terms ofa singular form may include plural forms unless referred to thecontrary.

In construing an element, the element is construed as including an erroror tolerance range even where no explicit description of such an erroror tolerance range. In describing a position relationship, when aposition relation between two parts is described as, for example, “on,”“over,” “under,” or “next,” one or more other parts may be disposedbetween the two parts unless a more limiting term, such as “just” or“direct(ly),” is used.

In describing a time relationship, when the temporal order is describedas, for example, “after,” “subsequent,” “next,” or “before,” a casewhich is not continuous may be included unless a more limiting term,such as “just,” “immediate(ly),” or “direct(ly),” is used.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure.

In describing elements of the present disclosure, the terms like“first,” “second,” “A,” “B,” “(a),” and “(b)” may be used. These termsare merely for differentiating one element from another element, and theessence, sequence, order, or number of a corresponding element shouldnot be limited by the terms. Also, when an element or layer is describedas being “connected,” “coupled,” or “adhered” to another element orlayer, the element or layer can not only be directly connected oradhered to that other element or layer, but also be indirectly connectedor adhered to the other element or layer with one or more interveningelements or layers “disposed” between the elements or layers, unlessotherwise specified.

The term “at least one” should be understood as including any and allcombinations of one or more of the associated listed items. For example,the meaning of “at least one of a first item, a second item, and a thirditem” denotes the combination of all items proposed from two or more ofthe first item, the second item, and the third item as well as the firstitem, the second item, or the third item.

In the description of embodiments, when a structure is described asbeing positioned “on or above” or “under or below” another structure,this description should be construed as including a case in which thestructures contact each other as well as a case in which a thirdstructure is disposed therebetween. The size and thickness of eachelement shown in the drawings are given merely for the convenience ofdescription, and embodiments of the present disclosure are not limitedthereto.

Features of various embodiments of the present disclosure may bepartially or overall coupled to or combined with each other, and may bevariously inter-operated with each other and driven technically as thoseskilled in the art can sufficiently understand. Embodiments of thepresent disclosure may be carried out independently from each other, ormay be carried out together in co-dependent relationship.

Reference will now be made in detail to the present disclosure, examplesof which are illustrated in the accompanying drawings.

FIG. 1 is a cross-sectional view showing a reflective liquid crystaldisplay device according to an embodiment of the present disclosure.

In FIG. 1, a reflective liquid crystal display device 110 according toan embodiment of the present disclosure includes first stack ST1, secondstack ST2, and third stack ST3 selectively reflecting red, green andblue colored lights, respectively, and a fourth stack ST4 determining anopaque mode or a transparent mode by absorbing or transmitting a light.

The first stack ST1 includes a first cholesteric liquid crystal (CLC)layer 126 between first and second substrates 120 and 142 facing andspaced apart from each other, the second stack ST2 includes a second CLClayer 148 between second and third substrates 142 and 154 facing andspaced apart from each other, and the third stack ST3 includes a thirdCLC layer 160 between third and fourth substrates 154 and 166 facing andspaced apart from each other.

The fourth stack ST4 includes an electrochromic layer 138 under thefirst substrate 120.

The first, second, third and fourth substrates 120, 142, 154 and 166 arespaced apart from and are parallel to one another. Each of the first,second, third and fourth substrates 120, 142, 154 and 166 includes aplurality of pixels P.

A first mode electrode 132, an ion storing layer 134, an electrolytelayer 136, the electrochromic layer 138, and a second mode electrode 140are sequentially disposed on of the entire first surface (a lowersurface) of the first substrate 120.

The first and second mode electrodes 132 and 140 supply a charge such asa hole and an electron to the electrochromic layer 138 due toapplication of a voltage. The first and second mode electrodes 132 and140 may be formed of a transparent conductive material such as indiumtin oxide (ITO) and indium zinc oxide (IZO).

The ion storing layer 134 reinforces a transmission force of the chargesuch as a hole and an electron. The ion storing layer 134 may be formedof an inorganic material having a relatively high ion conductivity suchas tin oxide (TO) doped with antimony (Sb).

The electrolyte layer 136 transmits the charge such as a hole and anelectron of the first and second mode electrodes 132 and 140 to theelectrochromic layer 138 due to application of a voltage. Theelectrolyte layer 136 may be formed of an electrolyte of a liquid phase,a quasi-solid phase or a solid phase.

The electrochromic layer 138 is oxidized or reduced due to the chargesuch as a hole and an electron to be colorized (opaque) or decolorized(transparent). As a result, the electrochromic layer 138 absorbs ortransmits a light. The electrochromic layer 138 may be formed of atransition metal oxide such as tungsten oxide (WO₃), molybdenum oxide(MoO₃) and titanium oxide (TiO₂) colorized due to a reduction andlithium nickel oxide (LiNiOx), vanadium oxide (V₂O₅) and iron oxide(IrO₂) colorized due to an oxidation.

The first mode electrode 132, the ion storing layer 134, the electrolytelayer 136, the electrochromic layer 138 and the second mode electrode140 under the first substrate 120 constitute the fourth stack ST4.

A first pixel electrode 122 is disposed in each pixel P on a secondsurface (an upper surface) of the first substrate 120, and a firstalignment layer 124 is disposed on an entire surface including the firstpixel electrode 122 of the first substrate 120.

A gate line, a data line and a thin film transistor (TFT) may bedisposed between the first substrate 120 and the first pixel electrode122.

A first common electrode 130 is disposed on an entire first surface (alower surface) of the second substrate 142, and a second alignment layer128 is disposed on an entire surface including the first commonelectrode 130 of the second substrate 142.

The first CLC layer 126 is disposed between the first and secondalignment layers 124 and 128. The first and second alignment layers 124and 128 initially align the first CLC layer 126. The first CLC layer 126reflects a red colored light of a predetermined circularly polarizedcomponent (a left-handed circularly polarized component or aright-handed circularly polarized component) among an incident externallight according to a voltage applied to the first pixel electrode 122and the first common electrode 130 and transmits a light of the othercomponents.

The first pixel electrode 122, the first alignment layer 124, the firstCLC layer 126, the second alignment layer 128 and the first commonelectrode 130 between the first and second substrates 120 and 142constitute the first stack ST1.

A second pixel electrode 144 is disposed in each pixel P on a secondsurface (an upper surface) of the second substrate 142, and a thirdalignment layer 146 is disposed on an entire surface including thesecond pixel electrode 144 of the second substrate 142.

A gate line, a data line and a thin film transistor (TFT) may bedisposed between the second substrate 142 and the second pixel electrode144.

A second common electrode 152 is disposed on an entire first surface (alower surface) of the third substrate 154, and a fourth alignment layer150 is disposed on an entire surface including the second commonelectrode 152 of the third substrate 154.

The second CLC layer 148 is disposed between the third and fourthalignment layers 146 and 150. The third and fourth alignment layers 146and 150 initially align the second CLC layer 148. The second CLC layer148 reflects a green colored light of a predetermined circularlypolarized component (a left-handed circularly polarized component or aright-handed circularly polarized component) among an incident externallight according to a voltage applied to the second pixel electrode 144and the second common electrode 152 and transmits a light of the othercomponents.

The second pixel electrode 144, the third alignment layer 146, thesecond CLC layer 148, the fourth alignment layer 150 and the secondcommon electrode 152 between the second and third substrates 142 and 154constitute the second stack ST2.

A third pixel electrode 156 is disposed in each pixel P on a secondsurface (an upper surface) of the third substrate 154, and a fifthalignment layer 158 is disposed on an entire surface including the thirdpixel electrode 156 of the third substrate 154.

A gate line, a data line and a thin film transistor (TFT) may bedisposed between the third substrate 154 and the third pixel electrode156.

A third common electrode 164 is disposed on an entire first surface (alower surface) of the fourth substrate 166, and a sixth alignment layer162 is disposed on an entire surface including the third commonelectrode 164 of the fourth substrate 166.

The third CLC layer 160 is disposed between the fifth and sixthalignment layers 158 and 162. The fifth and sixth alignment layers 158and 162 initially align the third CLC layer 160. The third CLC layer 160reflects a blue colored light of a predetermined circularly polarizedcomponent (a left-handed circularly polarized component or aright-handed circularly polarized component) among an incident externallight according to a voltage applied to the third pixel electrode 156and the third common electrode 164 and transmits a light of the othercomponents.

The third pixel electrode 156, the fifth alignment layer 158, the thirdCLC layer 160, the sixth alignment layer 162 and the third commonelectrode 164 between the third and fourth substrates 154 and 166constitute the third stack ST3.

Each of the first, second and third CLC layers 126, 148 and 160 includesa nematic liquid crystal and a chiral dopant to have a spiral structurewhere a director of the nematic liquid crystal rotates along a spiralaxis due to the chiral dopant and a layer of a pitch is repeated.

The first, second, third and fourth substrates 120, 142, 154 and 166 maybe formed of a glass or a flexible material such as a plastic.

In the reflective LCD device 110 according to an embodiment of thepresent disclosure, since the first, second and third stacks selectivelyreflecting the red, green and blue colored lights are formed by usingthe first, second, third and fourth substrates 120, 142, 154 and 166, avolume and a weight decrease and a fabrication cost is reduced.

The reflective LCD device 110 displays an image by using the red, greenand blue colored lights reflected by the first, second and third stacksST1, ST2 and ST3. These features will be illustrated with reference todrawings.

FIGS. 2A, 2B and 2C are cross-sectional views showing reflection of red,green and blue colored lights, respectively, of a reflective liquidcrystal display device according to an embodiment of the presentdisclosure.

In FIGS. 2A, 2B and 2C, first, second and third voltages V1, V2 and V3are applied to the first, second and third stacks ST1, ST2 and ST3,respectively, of the reflective LCD device 110 according to anembodiment of the present disclosure, thereby states of the first,second and third CLC layers 126, 148 and 160 adjusted. A fourth voltageV4 is applied to the fourth stack ST4, thereby a state of theelectrochromic layer 138 adjusted.

In FIG. 2A, in order for the reflective LCD device 110 to reflect thered colored light RL and not reflect the green and blue colored lightsGL and BL among a first white colored light WL1 incident from anexterior, the first voltage V1 is applied between the first pixelelectrode 122 and the first common electrode 130 of the first stack ST1,and a first CLC molecule 126 a of the first CLC layer 126 has a planarstate PS where a rotation surface of a director is disposed parallel tosurfaces of the first and second substrates 120 and 142.

The first CLC layer 126 of the planar state PS reflects the red coloredlight RL of a predetermined circularly polarized component (aleft-handed circularly polarized component or a right-handed circularlypolarized component) and transmits a light of the other components. Areflectance of the red colored light RL may be adjusted by changing amagnitude of the first voltage V1.

For example, the first voltage V1 may be equal to or greater than 0 Vand equal to or smaller than a maximum reflection voltage Vmr. The firstCLC layer 126 may display the red colored light RL of a maximum graylevel when the first voltage V1 is 0 V, and the first CLC layer 126 maydisplay the red colored light RL of a minimum gray level when the firstvoltage V1 is the maximum reflection voltage Vmr. When the first voltageV1 is between 0 V and the maximum reflection voltage Vmr, the first CLClayer 126 may display the red colored light RL of a gray level betweenthe maximum gray level and the minimum gray level.

The second voltage V2 is applied between the second pixel electrode 144and the second common electrode 152 of the second stack ST2, and asecond CLC molecule 148 a of the second CLC layer 148 has a homeotropicstate HS where a rotation surface of a director is disposedperpendicular to surfaces of the second and third substrates 142 and154.

The second CLC layer 148 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the second voltage V2 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The third voltage V3 is applied between the third pixel electrode 156and the third common electrode 164 of the third stack ST3, and a thirdCLC molecule 160 a of the third CLC layer 160 has a homeotropic state HSwhere a rotation surface of a director is disposed perpendicular tosurfaces of the third and fourth substrates 154 and 166.

The third CLC layer 160 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the third voltage V3 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The fourth voltage V4 is applied to between the first and second modeelectrodes 132 and 140 of the fourth stack ST4, and the electrochromiclayer 138 is oxidized or reduced according to an opaque mode or atransparent mode to be colorized or decolorized.

As a result, the red, green and blue colored lights RL, GL and BL of allof circularly polarized components (a left-handed circularly polarizedcomponent and a right-handed circularly polarized component) among thefirst white colored light WL1 incident from an exterior intactly passthrough the third and second CLC layers 160 and 148 of the homeotropicstate HS. The red colored light RL of a predetermined circularlypolarized component (a left-handed circularly polarized component or aright-handed circularly polarized component) among the first whitecolored light WL1 incident from an exterior is reflected by the firstCLC layer 126 of the planar state PS, and the light of the othercomponents intactly passes through the first CLC layer 126 of the planarstate PS. Accordingly, the reflective LCD device 110 emits the redcolored light RL to display a gray level corresponding to a red color.

In FIG. 2B, in order for the reflective LCD device 110 to reflect thegreen colored light GL and not reflect the red and blue colored lightsRL and BL among a first white colored light WL1 incident from anexterior, the second voltage V2 is applied between the second pixelelectrode 144 and the second common electrode 152 of the second stackST2, and a second CLC molecule 148 a of the second CLC layer 148 has aplanar state PS where a rotation surface of a director is disposedparallel to surfaces of the second and third substrates 142 and 154.

The second CLC layer 148 of the planar state PS reflects the greencolored light GL of a predetermined circularly polarized component (aleft-handed circularly polarized component or a right-handed circularlypolarized component) and transmits a light of the other components. Areflectance of the green colored light GL may be adjusted by changing amagnitude of the second voltage V2.

For example, the second voltage V2 may be equal to or greater than 0 Vand equal to or smaller than a maximum reflection voltage Vmr. Thesecond CLC layer 148 may display the green colored light GL of a maximumgray level when the second voltage V2 is 0 V, and the second CLC layer148 may display the green colored light GL of a minimum gray level whenthe second voltage V2 is the maximum reflection voltage Vmr. When thesecond voltage V2 is between 0 V and the maximum reflection voltage Vmr,the second CLC layer 148 may display the green colored light GL of agray level between the maximum gray level and the minimum gray level.

The first voltage V1 is applied between the first pixel electrode 122and the first common electrode 130 of the first stack ST1, and a firstCLC molecule 126 a of the first CLC layer 126 has a homeotropic state HSwhere a rotation surface of a director is disposed perpendicular tosurfaces of the first and second substrates 120 and 142.

The first CLC layer 126 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the first voltage V1 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The third voltage V3 is applied between the third pixel electrode 156and the third common electrode 164 of the third stack ST3, and a thirdCLC molecule 160 a of the third CLC layer 160 has a homeotropic state HSwhere a rotation surface of a director is disposed perpendicular tosurfaces of the third and fourth substrates 154 and 166.

The third CLC layer 160 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the third voltage V3 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The fourth voltage V4 is applied to between the first and second modeelectrodes 132 and 140 of the fourth stack ST4, and the electrochromiclayer 138 is oxidized or reduced according to an opaque mode or atransparent mode to be colorized or decolorized.

As a result, the red, green and blue colored lights RL, GL and BL of allof circularly polarized components (a left-handed circularly polarizedcomponent and a right-handed circularly polarized component) among thefirst white colored light WL1 incident from an exterior intactly passthrough the third CLC layer 160 of the homeotropic state HS. The greencolored light GL of a predetermined circularly polarized component (aleft-handed circularly polarized component or a right-handed circularlypolarized component) among the first white colored light WL1 incidentfrom an exterior is reflected by the second CLC layer 148 of the planarstate PS, and the light of the other components including the red andblue colored lights RL and BL intactly passes through the second CLClayer 148 of the planar state PS and the first CLC layer 126 of theplanar state PS. Accordingly, the reflective LCD device 110 emits thegreen colored light GL to display a gray level corresponding to a greencolor.

In FIG. 2C, in order for the reflective LCD device 110 to reflect theblue colored light BL and not reflect the red and green colored lightsRL and GL among a first white colored light WL1 incident from anexterior, the third voltage V3 is applied between the third pixelelectrode 156 and the third common electrode 164 of the third stack ST3,and a third CLC molecule 160 a of the third CLC layer 160 has a planarstate PS where a rotation surface of a director is disposed parallel tosurfaces of the third and fourth substrates 154 and 166.

The third CLC layer 160 of the planar state PS reflects the blue coloredlight BL of a predetermined circularly polarized component (aleft-handed circularly polarized component or a right-handed circularlypolarized component) and transmits a light of the other components. Areflectance of the blue colored light BL may be adjusted by changing amagnitude of the third voltage V3.

For example, the third voltage V3 may be equal to or greater than 0 Vand equal to or smaller than a maximum reflection voltage Vmr. The thirdCLC layer 160 may display the blue colored light BL of a maximum graylevel when the third voltage V3 is 0 V, and the third CLC layer 160 maydisplay the blue colored light BL of a minimum gray level when the thirdvoltage V3 is the maximum reflection voltage Vmr. When the third voltageV3 is between 0 V and the maximum reflection voltage Vmr, the third CLClayer 160 may display the blue colored light BL of a gray level betweenthe maximum gray level and the minimum gray level.

The first voltage V1 is applied between the first pixel electrode 122and the first common electrode 130 of the first stack ST1, and a firstCLC molecule 126 a of the first CLC layer 126 has a homeotropic state HSwhere a rotation surface of a director is disposed perpendicular tosurfaces of the first and second substrates 120 and 142.

The first CLC layer 126 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the first voltage V1 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The second voltage V2 is applied between the second pixel electrode 144and the second common electrode 152 of the second stack ST2, and asecond CLC molecule 148 a of the second CLC layer 148 has a homeotropicstate HS where a rotation surface of a director is disposedperpendicular to surfaces of the second and third substrates 142 and154.

The second CLC layer 148 of the homeotropic state HS transmits the red,green and blue colored light RL, GL and BL of all of circularlypolarized components (a left-handed circularly polarized component and aright-handed circularly polarized component).

For example, the second voltage V2 may be equal to or greater than aminimum transmission voltage Vmt. The minimum transmission voltage Vmtmay be greater than the maximum reflection voltage Vmr.

The fourth voltage V4 is applied to between the first and second modeelectrodes 132 and 140 of the fourth stack ST4, and the electrochromiclayer 138 is oxidized or reduced according to an opaque mode or atransparent mode to be colorized or decolorized.

As a result, the blue colored light BL of a predetermined circularlypolarized component (a left-handed circularly polarized component or aright-handed circularly polarized component) among the first whitecolored light WL1 incident from an exterior is reflected by the thirdCLC layer 160 of the planar state PS, and the light of the othercomponents including the red and green colored lights RL and GL intactlypasses through the third CLC layer 160 of the planar state PS and thesecond and first CLC layers 148 and 126 of the homeotropic state.Accordingly, the reflective LCD device 110 emits the blue colored lightBL to display a gray level corresponding to a blue color.

The reflective LCD device 110 according to an embodiment of the presentdisclosure displays an image by using the red, green and blue coloredlights RL, GL and BL reflected by the first, second and third stacksST1, ST2 and ST3, respectively.

The first, second and third stacks ST1, ST2 and ST3 may be driventhrough a time division method or may be driven simultaneously.

The reflective LCD device 110 may be driven in an opaque mode or atransparent mode by using the fourth stack ST4. These features will beillustrated with reference to drawings.

FIGS. 3A and 3B are cross-sectional views showing an opaque mode and atransparent mode, respectively, of a reflective liquid crystal displaydevice according to an embodiment of the present disclosure. The first,second and third stacks ST1, ST2 and ST3 may be exemplarily drivensimultaneously.

In FIG. 3A, the reflective LCD device 110 according to an embodiment ofthe present disclosure is driven in an opaque mode. The first, secondand third voltages V1, V2 and V3 are applied to the first, second andthird stacks ST1, ST2 and ST3, respectively, such that each of thefirst, second and third CLC layers 126, 148 and 160 has the planar statePS. The fourth voltage V4 is applied to the fourth stack ST4 such thatthe electrochromic layer 138 is oxidized or reduced to be colorized(opaque).

As a result, the red, green and blue colored lights RL, GL and BL of apredetermined circularly polarized component (a left-handed circularlypolarized component or a right-handed circularly polarized component)among the first white colored light WL1 incident to the reflective LCDdevice 110 from an exterior are reflected by the first, second and thirdCLC layers 126, 148 and 160, respectively, and the light of the othercomponents is absorbed by the electrochromic layer 138.

For example, when the reflective LCD device 110 displays black color,the first, second and third stacks ST1, ST2 and ST3 may not reflect thered, green and blue colored lights RL, GL and BL, respectively, and theelectrochromic layer 138 may absorb all of the first white colored lightWL1. As a result, a contrast ratio is improved.

In addition, a second white colored light WL2 incident to a lowersurface of the reflective LCD device 110 from an exterior may beabsorbed by the electrochromic layer 138.

Accordingly, in the opaque mode, the reflective LCD device 110 displaysan image with a background incident to the lower surface blocked.

In FIG. 3B, the reflective LCD device 110 according to an embodiment ofthe present disclosure is driven in a transparent mode. The first,second and third voltages V1, V2 and V3 are applied to the first, secondand third stacks ST1, ST2 and ST3, respectively, such that each of thefirst, second and third CLC layers 126, 148 and 160 has the planar statePS. The fourth voltage V4 is applied to the fourth stack ST4 such thatthe electrochromic layer 138 is reduced or oxidized be decolorized(transparent).

As a result, the red, green and blue colored lights RL, GL and BL of apredetermined circularly polarized component (a left-handed circularlypolarized component or a right-handed circularly polarized component)among the first white colored light WL1 incident to the reflective LCDdevice 110 from an exterior are reflected by the first, second and thirdCLC layers 126, 148 and 160, respectively, and the light of the othercomponents intactly passes through the electrochromic layer 138.

In addition, the red, green and blue colored lights RL, GL and BL of apredetermined circularly polarized component (a left-handed circularlypolarized component or a right-handed circularly polarized component)among the second white colored light WL2 incident to a lower surface ofthe reflective LCD device 110 from an exterior may be reflected by thefirst, second and third CLC layers 126, 148 and 160, respectively, andthe light of the other components may intactly pass through theelectrochromic layer 138 and the first, second and third CLC layers 126,148 and 160 to be emitted as a third white light WL3 through an uppersurface of the reflective LCD device 110.

Accordingly, in the transparent mode, the reflective LCD device 110displays an image with a background incident to the lower surface.

The reflective LCD device 110 according to an embodiment of the presentdisclosure displays an image using an external light without a backlightunit. The reflective LCD device 110 blocks or transmits the backgroundimage using the fourth stack ST4 including the electrochromic layer 138.Accordingly, the reflective LCD device 110 may be applied to a smartwindow which displays an image and functions as a window.

The first to sixth alignment layers 124, 128, 146, 150, 158 and 162 ofthe reflective LCD device 110 may be formed through a single irradiationof an ultraviolet ray using a self-alignment monomer.

FIGS. 4A to 4F are cross-sectional views showing a method of fabricatinga reflective liquid crystal display device according to an embodiment ofthe present disclosure.

In FIG. 4A, the first mode electrode 132, the ion storing layer 134, theelectrolyte layer 136, the electrochromic layer 138, and the second modeelectrode 140 are sequentially formed on the entire first surface (thelower surface) of the first substrate 120 to constitute the fourth stackST4.

The first pixel electrode 122 is formed in each pixel P on the secondsurface (the upper surface) of the first substrate 120.

In FIG. 4B, the first common electrode 130 is formed on the entire firstsurface (the lower surface) of the second substrate 142, and the secondpixel electrode 144 is formed in each pixel P on the second surface (theupper surface) of the second substrate 142.

Next, the first and second substrates 120 and 142 are attached, and thefirst CLC layer 126 is formed between the first and second substrates120 and 142 with a mixed material of the first CLC molecule 126 a andthe self-alignment monomer 170 to constitute the first stack ST1.

For example, after the first and second substrates 120 and 142 areattached, the first CLC layer 126 may be formed through an injectingmethod. Alternatively, after the first CLC layer 126 is formed on one ofthe first and second substrates 120 and 142 through a dispensing method,the first and second substrates 120 and 142 may be attached.

The first CLC molecule 126 a of the first CLC layer 126 has a focalconic state FS where a rotation surface of a director is randomlydisposed with respect to the surfaces of the first and second substrates120 and 142.

The self-alignment monomer 170 may include a material expressed by thefollowing chemical formulas 1 to 4 including a cinnamate group or achalcone group.

Polyvinyl-cinnamate in chemical formula 1 may be polymerized by apolarized ultraviolet ray having a wavelength of about 330 nm and anenergy density of about 3 J/cm², and trans-cinnamate in chemical formula2 may be polymerized by a polarized ultraviolet ray having a wavelengthof about 330 nm and an energy density of about 4 J/cm².4-hydroxy-chalcone in chemical formula 3 may be polymerized by apolarized ultraviolet ray having a wavelength of about 365 nm and anenergy density of about 3 J/cm², and 4′-hydroxy-chalcone in chemicalformula 4 may be polymerized by a polarized ultraviolet ray having awavelength of about 365 nm and an energy density of about 4 J/cm².

In FIG. 4C, the second common electrode 152 is formed on the entirefirst surface (the lower surface) of the third substrate 154, and thethird pixel electrode 156 is formed in each pixel P on the secondsurface (the upper surface) of the third substrate 154.

Next, the second and third substrates 142 and 154 are attached, and thesecond CLC layer 148 is formed between the second and third substrates142 and 154 with a mixed material of the second CLC molecule 148 a andthe self-alignment monomer 170 to constitute the second stack ST2.

For example, after the second and third substrates 142 and 154 areattached, the second CLC layer 148 may be formed through an injectingmethod. Alternatively, after the second CLC layer 148 is formed on oneof the second and third substrates 142 and 154 through a dispensingmethod, the second and third substrates 142 and 154 may be attached.

Since a repetition pitch of the CLC molecule is proportional to awavelength of the reflected light, the repetition pitch of the secondCLC molecule 148 a of the second CLC layer 148 reflecting the greencolored light GL is smaller than the repetition pitch of the first CLCmolecule 126 a of the first CLC layer 126 reflecting the red coloredlight RL, and the second CLC molecule 148 a of the second CLC layer 148has the focal conic state FS where a rotation surface of a director israndomly disposed with respect to surfaces of the second and thirdsubstrates 142 and 154.

The self-alignment monomer 170 of the second CLC layer 148 may be thesame as the self-alignment monomer 170 of the first CLC layer 126.

In FIG. 4D, the third common electrode 164 is formed on the entire firstsurface (the lower surface) of the fourth substrate 166.

Next, the third and fourth substrates 154 and 166 are attached, and thethird CLC layer 160 is formed between the third and fourth substrates154 and 166 with a mixed material of the third CLC molecule 160 a andthe self-alignment monomer 170 to constitute the third stack ST3.

For example, after the third and fourth substrates 154 and 166 areattached, the third CLC layer 160 may be formed through an injectingmethod. Alternatively, after the third CLC layer 160 is formed on one ofthe third and fourth substrates 154 and 166 through a dispensing method,the third and fourth substrates 154 and 166 may be attached.

The repetition pitch of the third CLC molecule 160 a of the third CLClayer 160 reflecting the blue colored light BL is smaller than therepetition pitch of the second CLC molecule 148 a of the second CLClayer 148 reflecting the green colored light GL, and the third CLCmolecule 160 a of the third CLC layer 160 has the focal conic state FSwhere a rotation surface of a director is randomly disposed with respectto surfaces of the third and fourth substrates 154 and 166.

The self-alignment monomer 170 of the third CLC layer 160 may be thesame as the self-alignment monomer 170 of the first and second CLClayers 126 and 148.

In FIG. 4E, a linearly polarized ultraviolet ray is irradiated onto thefirst, second and third CLC layers 126, 148 and 160 through the fourthsubstrate 166 of the attached first, second, third and fourth substrates120, 142, 154 and 166 one time. The self-alignment monomer 170 of thefirst, second and third CLC layers 126, 148 and 160 is polymerized by asingle irradiation of the polarized ultraviolet ray.

Since the fourth stack ST4 is formed on the first surface (the lowersurface) of the first substrate 120, the polarized ultraviolet ray maybe irradiated onto the first, second and third CLC layers 126, 148 and160 through the fourth substrate 166.

In FIG. 4F, due to polymerization of the self-alignment monomer 170according to a single irradiation of the polarized ultraviolet ray, thefirst alignment layer 124 is formed between the first substrate 120 andthe first CLC layer 126, the second alignment layer 142 is formedbetween the second substrate 142 and the first CLC layer 126, the thirdalignment layer 146 is formed between the second substrate 142 and thesecond CLC layer 148, the fourth alignment layer 150 is formed betweenthe third substrate 154 and the second CLC layer 148, the fifthalignment layer 158 is formed between the third substrate 154 and thethird CLC layer 160, and the sixth alignment layer 162 is formed betweenthe fourth substrate 166 and the third CLC layer 160.

The first CLC layer 126 has the planar state PS where a rotation surfaceof a director is disposed parallel to surfaces of the first and secondsubstrates 120 and 142 due to an initial alignment direction by thefirst and second alignment layers 124 and 128. The second CLC layer 148has the planar state PS where a rotation surface of a director isdisposed parallel to surfaces of the second and third substrates 142 and154 due to an initial alignment direction by the third and fourthalignment layers 146 and 150. The third CLC layer 160 has the planarstate PS where a rotation surface of a director is disposed parallel tosurfaces of the third and fourth substrates 154 and 166 due to aninitial alignment direction by the fifth and sixth alignment layers 158and 162.

In the method of fabricating the reflective LCD device 110 according toan embodiment of the present disclosure, since the first, second, third,fourth, fifth and sixth alignment layers 124, 128, 146, 150, 158 and 162are formed by the single irradiation of the polarized ultraviolet ray,the fabrication process is simplified and the fabrication time and thefabrication cost are reduced.

After the first, second, third and fourth substrates 120, 142, 154 and166 are attached, the first, second, third, fourth, fifth and sixthalignment layers 124, 128, 146, 150, 158 and 162 are formed by thesingle irradiation of the polarized ultraviolet ray. As a result, theoptical axes of the first, second and third CLC layers 126, 148 and 160are aligned with each other, and a contrast ratio and a color purity areimproved. In addition, since an error of an alignment direction due tomisalignment of the attachment is reduced, generation of a twist angleis prevented and a driving voltage is reduced.

For example, the first, second and third stacks ST1, ST2 and ST3 may bedriven with a voltage smaller than about 20 V.

Further, the first, second, third, fourth, fifth and sixth alignmentlayers 124, 128, 146, 150, 158 and 162 are formed by the singleirradiation of the polarized ultraviolet ray, and the first, second andthird CLC layers 126, 148 and 160 are aligned by the single irradiationof the polarized ultraviolet ray to have the planar state PS. As aresult, the first, second and third CLC layers 126, 148 and 160 aresufficiently aligned even with first, second, third, fourth, fifth andsixth alignment layers 124, 128, 146, 150, 158 and 162 each having arelatively small thickness. Accordingly, a transmittance of the first,second and third CLC layers 126, 148 and 160 increases and a scatteringof the first, second and third CLC layers 126, 148 and 160 decreases.

For example, each of the first, second, third, fourth, fifth and sixthalignment layers 124, 128, 146, 150, 158 and 162 may have a thickness ofabout 20 nm.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of fabricating a reflective liquidcrystal display device, comprising: forming a first mode electrode, anion storing layer, an electrolyte layer, an electrochromic layer, and asecond mode electrode sequentially on an entire lower surface of a firstsubstrate; forming a first pixel electrode in each of a plurality ofpixels on an upper surface of the first substrate; forming a firstcommon electrode on an entire lower surface of a second substrate;forming a second pixel electrode in each of the plurality of pixels onan upper surface of the second substrate; forming a first cholestericliquid crystal layer between the first and second substrates with amixed material of a first cholesteric liquid crystal molecule and aself-alignment monomer; forming a second common electrode on an entirelower surface of a third substrate; forming a third pixel electrode ineach of the plurality of pixels on an upper surface of the thirdsubstrate; forming a second cholesteric liquid crystal layer between thesecond and third substrates with a mixed material of a secondcholesteric liquid crystal molecule and the self-alignment monomer;forming a third common electrode on an entire lower surface of a fourthsubstrate; forming a third cholesteric liquid crystal layer between thethird and fourth substrates with a mixed material of a third cholestericliquid crystal molecule and the self-alignment monomer; and forming afirst alignment layer between the first substrate and the firstcholesteric liquid crystal layer, a second alignment layer between thesecond substrate and the first cholesteric liquid crystal layer, a thirdalignment layer between the second substrate and the second cholestericliquid crystal layer, a fourth alignment layer between the thirdsubstrate and the second cholesteric liquid crystal layer, a fifthalignment layer between the third substrate and the third cholestericliquid crystal layer, and a sixth alignment layer between the fourthsubstrate and the third cholesteric liquid crystal layer by irradiatinga polarized ultraviolet ray onto the first, second and third cholestericliquid crystal layers.
 2. The method of claim 1, further comprisingattaching the first, second, third and fourth substrates before thepolarized ultraviolet ray is irradiated.
 3. The method of claim 1,wherein the first, second, third, fourth, fifth and sixth alignmentlayers are formed by polymerization of the self-alignment monomer due tothe polarized ultraviolet ray.
 4. The method of claim 1, wherein thefirst cholesteric liquid crystal layer has a planar state due to thefirst and second alignment layers such that a rotation surface of adirector is disposed parallel to surfaces of the first and secondsubstrate, wherein the second cholesteric liquid crystal layer has aplanar state due to the third and fourth alignment layers such that arotation surface of a director is disposed parallel to surfaces of thesecond and third substrate, and wherein the third cholesteric liquidcrystal layer has a planar state due to the fifth and sixth alignmentlayers such that a rotation surface of a director is disposed parallelto surfaces of the third and fourth substrate.
 5. The method of claim 1,wherein a repetition pitch of the second cholesteric liquid crystalmolecule is smaller than a repetition pitch of the first cholestericliquid crystal molecule and greater than a repetition pitch of the thirdcholesteric liquid crystal molecule.
 6. A method of fabricating areflective liquid crystal display device, comprising: providing first,second, third and fourth substrates spaced apart from and parallel toeach other; forming a first cholesteric liquid crystal layer between thefirst and second substrates with a mixed material of a first cholestericliquid crystal molecule and a self-alignment monomer; forming a secondcholesteric liquid crystal layer between the second and third substrateswith a mixed material of a second cholesteric liquid crystal moleculeand the self-alignment monomer; forming a third cholesteric liquidcrystal layer between the third and fourth substrates with a mixedmaterial of a third cholesteric liquid crystal molecule and theself-alignment monomer; and forming a first alignment layer between thefirst substrate and the first cholesteric liquid crystal layer, a secondalignment layer between the second substrate and the first cholestericliquid crystal layer, a third alignment layer between the secondsubstrate and the second cholesteric liquid crystal layer, a fourthalignment layer between the third substrate and the second cholestericliquid crystal layer, a fifth alignment layer between the thirdsubstrate and the third cholesteric liquid crystal layer and a sixthalignment layer between the fourth substrate and the third cholestericliquid crystal layer by irradiating a polarized ultraviolet ray onto thefirst, second and third cholesteric liquid crystal layers.
 7. The methodof claim 6, further comprising: sequentially forming a first modeelectrode, an ion storing layer, an electrolyte layer, an electrochromiclayer and a second mode electrode on a whole of a lower surface of thefirst substrate and forming a first pixel electrode in each of aplurality of pixels on an upper surface of the first substrate; forminga first common electrode on a whole of a lower surface of the secondsubstrate and forming a second pixel electrode in each of the pluralityof pixels on an upper surface of the second substrate; forming a secondcommon electrode on a whole of a lower surface of the third substrateand forming a third pixel electrode in each of the plurality of pixelson an upper surface of the third substrate; and forming a third commonelectrode on a whole of a lower surface of the fourth substrate.